Up-potting is simply the process of putting your seedling in a larger pot from a smaller pot. This is done so the plant has more room to grow before you plant it out in your garden. Up-potting is most commonly done to tomatoes but can be done to any seedling that is not quite ready to go in the garden but needs more space to grow.
I generally wait to up-pot my seedlings until they have their first set of true leaves.
The leaves that come out of the ground on the original sprout are not true leaves, they will eventually die back. The set of leaves that grows out of the original sprouted leaves are the true leaves. As seen above they are more intricate. Once your seedlings have their first set of true leaves it is likely time to up pot.
First, you will want to fill your larger pots with your chosen potting soils (I also top mine with worm castings) and have them ready for your seedlings.
The next step in up-potting your seedling is gently removing it from its cell, or pot. Since my seedlings are in a large multi-cell tray I use a plastic tool that came with the trays to remove my seedlings. You can also just use a fork or popsicle stick. You just gently lift the seedling block out of the cell for transplant.
I generally start my seeds with two seeds in each cell. If I get two sprouts you need to gently separate the two seedlings when I up-pot them and give them each their own new pot.
I start by rubbing some of the soil off the base of the roots, then gently pull the two seedlings apart.
Next, you will need to make a small hole in the soil of your larger pots that you will then place your seedling in. Once you have a spot for your seedling you will gently place your seedling in the hole and fill the hole with soil and lightly compress the soil down around the seedling.
Once your seedling is in its new home be sure to give it some water right away and then you are done!
Don't forget to label it as well!